1. Field of the Invention
The present invention relates generally to press vibration monitoring, and, more particular, to a method of reducing dynamic factors during press operation, thereby lowering production press vibration severity levels.
2. Description of the Related Art
It has been found through experimentation that as press speed increases there are many additional die loads that occur that are not present at slower press speeds. There are actually several additional sources of significant die loads that, in general, many press owners, manufacturers, and operators do not know exist. At higher speeds, even though not exceeding the capacity of the press, the press requires more force to make the output part, and must also contend with several additional forces, which in turn creates a different set of more severe vibration conditions.
Vibration stress magnifications, created by the multiple dynamic load increases, can cause many problems with press structures. At certain definable vibration severity levels, as described in U.S. Pat. No. 5,094,107, stress magnification levels will be present, thus creating increased maintenance problems for the press and tooling. Vibration monitoring systems of the prior art shut down the press at an individual predetermined level, which when reached would begin to cause long term reliability damage to the press.
U.S. Pat. No. 5,094,107 measures this vibration severity while in actual production, and allows the press operator and production manager to know the long term liability effects of running the press at any combination of sensed speed and load. By monitoring the actual vibration severity level of the die application, and comparing the corresponding operation vibration severity level to a previously produced vibration severity zone chart, either manually or electronically the long term press operation may be graded.
What is needed in the art is a methodology for detecting and detailing the particular die process functions that create production press vibration severity levels and tipping moment conditions during increased speed operation. By reducing such production press vibration severity levels, increased productivity, reliability and optimization of existing metal forming dies may result.
According to the present invention, the press for use with an existing metal die is used to identify the rate of escalation of vibration severity and/or tipping moment as production speed is increased. The system utilizes and creates a data set regarding a trend path of the press and tool by monitoring press speed versus vibration severity and other parameters.
The present invention, in one form thereof, identifies the details of vibration acceleration levels at different press operating speeds, thereby identifying attributing factors that add or multiply, to create an overall vibration severity level. After such data is acquired, concentration and optimization on major contributing parameters is utilized to reduce portions of the vibration severity curve.
The invention, in another form thereof, includes a method for determining die tipping conditions with a vibration severity monitoring apparatus. Conditions regarding the slide stripper plate, or bed tipping and die station activity may all be monitored, recorded, and analyzed with the present invention.
The invention, in one form thereof, is directed to a method of monitoring the operation of a press machine which is run through a plurality of press running cycles. According to the method, there is first defined a plurality of press operating events associated with the operation of the press machine. Each of these press operating events has an associated modifiable control function. For each one of the press operating events, there is provided a measure of the vibrational activity associated therewith that is present in the press machine during each one of the press running cycles. A vibration measurement signal is generated which is representative of the vibrational activity measurement. The vibration measurement signals associated with each press operating event are then processed to identify the presence of a vibration trend therein that meets a defined trending criteria. The respective control function of each press operating event that is associated with the identification of the vibration trend is then modified.
The press operating events include, but are not limited to, stripper plate impact on the downstroke of the press machine slide, punch impact on a workpiece, snap-through activity, and stripper plate impact on the upstroke of the press machine slide.
The vibrational activity measurements are preferably generated by an arrangement of accelerometers coupled to the press machine.
The predefined trending criteria, in one form thereof, involves a rate of change in the vibration measurement signals that exceeds a predetermined threshold level.
The monitoring method is preferably applied to a press machine that is run through press running cycles characterized by a variable press running speed. Alternately, the press running cycles may be characterized by a variable load developed within the press machine.
The invention, in another form thereof, is directed to a method of monitoring the operation of a press machine which is run through a plurality of press running cycles. According to the method, there is first provided a respective measure of the vibrational activity that is present in the press machine during each one of the press running cycles. There is generated a respective vibration measurement signal which is representative of the vibrational activity measurement. Next, there is defined a plurality of press operating events which are associated with the operation of the press machine, wherein each press operating event has an associated modifiable control function. The respective vibration measurement signal associated with each one of the press running cycles is then resolved into a corresponding set of component vibration signals each associated with a respective one of the press operating events. The respective set of component vibration signals associated with each one of the press running cycles is processed to identify the presence of a vibration trend therein that meets a defined trending criteria. This identification of the vibration trend is made in relation to component vibration signals that are associated with the same press operating event. The respective control function of each press operating event which corresponds to the component vibration signals associated with identification of the vibration trend is then suitably modified.
The monitoring method, in another form thereof, further involves correlating the respective vibration measurement signal associated with each one of the press running cycles to a preselected press operating parameter; and correlating the occurrence of each one of the press operating events to the preselected press operating parameter. These correlation operations facilitate the correlation of the respectively corresponding set of component vibration signals of each respective vibration measurement signal to respective ones of the plurality of press operating events. The preselected press operating parameter preferably includes a measure of the press machine slide displacement relative to bottom dead center.
The invention, in another form thereof, is directed to a system for monitoring the operation of a press machine over a plurality of press running cycles. The system includes a means for defining a plurality of press operating events associated with the operation of the press machine, wherein each respective one of the press operating events has a modifiable control function associated therewith. The system further includes a measurement means for providing, with respect to each one of the press operating events, a respective measure of the vibrational activity associated therewith that is present in the press machine during each one of the press running cycles, and for generating a respective vibration measurement signal representative thereof. A processor means processes the respective vibration measurement signals associated with each one of the press operating events to identify the presence of a vibration trend therein that meets a defined trending criteria and to generate trend identification signals representative thereof. A controller means, which is responsive to the trend identification signals generated by the processor means, modifies the respective control function of each press operating event which is associated with identification of the vibration trend.
The press operating events include stripper plate impact on the downstroke of the press machine slide, punch impact on a workpiece, snap-through activity, and stripper plate impact on the upstroke of the press machine slide.
The measurement means further includes at least one accelerometer coupled to the press machine.
The defined trending criteria involves a rate of change in the vibration measurement signals that exceeds a predetermined threshold level.
The press running speed is preferably varied over the plurality of press running cycles. Alternately, the load developed within the press machine is varied over the plurality of press running cycles.
The invention, in another form thereof, is directed to a system for monitoring the operation of a press machine over a plurality of press running cycles. A measurement means provides a respective measure of the vibrational activity that is present in the press machine during each one of the press running cycles and generates a respective vibration measurement signal representative thereof. There is also provided a means for defining a plurality of press operating events which are associated with the operation of the press machine, wherein each one of the press operating events has a modifiable control function associated therewith. A signal resolving means resolves the respective vibration measurement signal associated with each one of the press running cycles into a corresponding set of component vibration signals each associated with a respective one of the press operating events. A processor means processes the respective set of component vibration signals associated with each one of the press running cycles to identify the presence of a vibration trend therein that meets a defined trending criteria and to generate trend identification signals representative thereof. This vibration trend identification is made in relation to component vibration signals which are associated with the same press operating event. A control means, which is responsive to the trend identification signals generated by the processor means, modifies the respective control function of each press operating event which corresponds to the component vibration signals that are associated with identification of the vibration trend.
The system, in one form thereof, further includes a first correlation means for correlating the respective vibration measurement signal associated with each one of the press running cycles to a preselected press operating parameter and for generating a first correlation signal group representative thereof; and a second correlation means for correlating the occurrence of each one of the press operating events to the preselected press operating parameter and for generating a second correlation signal group representative thereof. There is also provided a third correlation means, which is responsive to the first correlation signal group generated by the first correlation means and to the second correlation signal group generated by the second correlation means, for correlating the respectively corresponding set of component vibration signals of each respective vibration measurement signal to respective ones of the press operating events.
The preselected press operating parameter includes a measure of the press machine slide displacement relative to bottom dead center.
The invention, in yet another form thereof, is directed to a method of monitoring the operation of a press machine having an operatively movable press member. According to the method, there is defined at least two load measurement locations associated with the movable press member. There is provided a measure of the load developed within the movable press member at each respective one of the at least two load measurement locations. Load measurement signals representative of the load measurements are generated. A determination is made of the tipping moment experienced by the movable press member based upon the generated load measurement signals. The determined tipping moment is then evaluated relative to a predefined tipping moment severity level.
The step of provided the load measurements involves providing a respective load sensor coupled to the movable press member at each respective one of the at least two load measurement locations. The movable press member includes at least one of a press machine slide and a press machine stripper plate.
In one form, the at least two load measurement locations include a first measurement location and a second measurement location each configured at a respective lateral side of the movable press member. In another form, the at least two load measurement locations include a first measurement location and a second measurement location each respectively configured at a forward side and a rearward side of the movable press member.
In another form, the at least two load measurement locations include a pair of measurement locations spaced equidistantly from a reference axis. Determining the tipping moment further involves computing the difference between the respective load measurement signals associated with each respective one of the pair of measurement locations and generating a difference signal representative thereof; and computing the tipping moment as a function of the generated difference signal and the displacement of either one of the pair of measurement locations relative to the reference axis.
The press machine monitoring activity preferably occurs substantially continuously over at least the duration of the press machine slide travel.
Evaluation of the tipping moment preferably involves controlling the operation of the movable press member in accordance with the evaluation results.
The invention, in still yet another form thereof, is directed to a system for monitoring the operation of a press machine having an operatively movable press member. A measurement means provides a measure of the load developed within the movable press member at each respective one of at least two load measurement locations thereof and generates load measurement signals representative thereof. A processor means, which is responsive to the load measurement signals generated by the measurement means, determines a tipping moment experienced by the movable press. An evaluation means evaluates the determined tipping moment relative to a predefined tipping moment severity level.
The processor means further includes a first means for computing the difference between the respective load measurement signals associated with each respective one of a pair of measurement locations and generating a difference signal representative thereof; and a second means for computing the tipping moment as a function of the generated difference signal and the displacement of either one of the pair of measurement locations relative to a reference axis.
The evaluation means further includes a controller to control the operation of the movable press member in accordance with the evaluation results.